The invention relates to an exhaust gas recycling system for an exhaust gas turbocharged internal combustion engine for propelling a motor vehicle. The invention is especially concerned with an engine having an exhaust gas turbine driven air compressor, the exhaust gas line up-stream of the turbine being connected by an exhaust gas recycling line with an engine charging air line downstream of the compressor. An exhaust gas recycling valve is arranged in the exhaust gas recycling line for accommodating mixing of exhaust gas with the charging air when a control valve adjusts a lower pressure in the charging air line than in the exhaust gas line.
An exhaust gas recycling system of the above-mentioned kind is known from U.S. Pat. No. 3,925,989. In this arrangement a control valve is disposed in the exhaust gas line which is operated in dependance on the engine operating conditions to block out more or less of the flow of exhaust gas to the turbine and thereby adjust a higher pressure in the exhaust gas line than in the charging line. As a result of the higher pressure in the exhaust gas line, the exhaust gas can be mixed with the charging air by passing through an exhaust gas recycling line and a spring loaded one-way valve arranged therein. With this arrangement, the spring loaded one-way valve is so adjusted that a mixture of the exhaust gas with the charging air first occurs above a predetermined pressure difference between the exhaust and charging lines.
The known exhaust gas recycling system has the disadvantage that the volume of exhaust gas to be mixed with the charging air is only controlled as a function of the pressure ratio between the exhaust and charging air lines in such a manner that a varying recycling of the exhaust gas is not possible. Furthermore, the desired mixing of exhaust gas is obtained through structural measures at the exhaust gas side of the engine where valuable and expensive component parts must be installed. Finally, there is the disadvantage that the rotational speed of the turbocharger is reduced during operation with exhaust gas recycling so that with an acceleration from a part-load condition of the engine, the charging pressure build-up is delayed.
The invention is based upon the problem to improve the known exhaust gas recycling systems so that an optimally precise controlled exhaust gas volume can be mixed with the charging air for all respective desired operating ranges of the engine. Thereby, one can achieve the highest possible reduction in the NOx-(Nitrous oxide) emissions, no or only a very small increase in the CO-(Carbon monoxide), HC-(Hydrocarbon) and particle emissions, and no or only an insignificant increase in the fuel consumption.
The problem is inventively solved by providing a valve in a compressor bridging bypass line connected to the charging air line, which valve is controlled, by itself or together with an exhaust recycling valve, as a function of the operating conditions of the internal combustion engine of the motor vehicle.
The exhaust gas recycling system according to the invention has the advantage that not only the pressure ratio between the charging air line and the exhaust gas line, but also the exhaust gas recirculation volume, can be made to optimally correspond to the respective operating condition of the internal combustion engine and thereby result in a maximum possible reduction in NOx emissions with only minimal changes in the efficiency and in the remaining emissions. These results can be achieved with corresponding adjustment of the valve control characteristics to match the engine operating conditions.
A further advantage consists in that because of the control at the compressor side of the engine, the pressure drop at the turbocharger and its rotational speed is only decreased by the smallest possible amount, whereby during acceleration out of the part-load region, the charging pressure build-up can be accomplished in the smallest time. Finally, there is the advantage that the compressor side pressure control can be obtained in a simple manner with economical components.
An especially simple embodiment of the invention is obtained if the bypass line is integrated into the compressor housing of the exhaust gas turbocharger and the control valve is likewise mounted at the compressor housing.
Further objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, one embodiment in accordance with the present invention .